A conventional device for controlling a wiper by injecting an LED light or the like onto a detection surface provided on a windshield and by receiving a reflected light by a light receiving element and by performing control based on an output signal of the light receiving element. In this device, as the JP-A-4-349053, as a means for reflecting the sense of each of a driver to determination of intermittence time, a sensitivity adjustment volume is provided. The adjustment by this sensitivity adjustment volume has, as shown in FIG. 1, three types of intermittence time which can be chosen for one rainfall state, and either of short, medium or long is chosen based on the position of the sensitivity adjustment volume set manually by the driver.
In the meantime, a method for detecting dynamic adhesion of raindrops (JP-A-2001-180447) and a method for evaluating fluctuation of an output signal of a light receiving element (JP-A-2002-277386) are presented by the inventors. Also, as conventional examples of a method for detecting raindrops, a method for detecting the raindrop in comparison with a reference value (so-called threshold value method) (JP-A-61-37560, for example) and a method for detecting raindrops by an integrated value of the light receiving element output (so-called integration method) (JP-A-4-349053, for example) are disclosed.
These wiper control devices are required to perform smooth wiper wiping operation following the rainfall situation. Simply speaking, it is necessary to perform wiping when it begins to rain, while wiping should be stopped when rain is ended. In the meantime, actual rainfall situations are not such simple but changed in various ways according to rainfall, air flow, driving speed, etc.
Moreover, when a vehicle is running, it may pass through an environment where rainfall is shut off as in a tunnel. When passing through such a rainfall shutoff environment, the rainfall situation changes before entrance to the tunnel, during driving in the tunnel and after exit from the tunnel. Particularly, the rainfall situation is rapidly changed at entrance to the tunnel and exit therefrom.
Also, a conventional device for controlling a wiper by injecting an LED light or the like onto a detection surface provided on a windshield and performing control based on the light amount of its reflected light. In this device, the area of the above detection surface is extremely smaller than the total area of the windshield. Therefore, in order to improve the accuracy, a method for determining intermittence of a wiper based on a water amount carried by the wiper through wiping is proposed (International Publication No. WO 91/03393).
The invention described in International Publication No. WO 91/03393 is based on the assumption that the size of a wall of water pushed out by a sweeping wiper blade can give accurate and reliable measurement of rainfall on the windscreen between a continuous sweeping stroke of the wiper blade.
However, this assumption of the size of water wall=rainfall is not applicable to all the driving scenes. The wiper blade after wiping the raindrops is wet itself, and the water wall is formed also by the water adhering to this blade. This wall is not made from water collected by wiping but detected by the device without distinction. Also, the water supplied onto the windshield is not limited to rainfall. In a vehicle, for example, such phenomena are observed that water is dripping from an upper part of the wiping area of the wiper (roof and the like) and that water wiped out to the outside of the area is dripping after some time (hereinafter such dripping water is called as “dripping water”).
To explain it in more concrete, assume a case where a vehicle enters a tunnel in the rainfall situation that raindrops with a somewhat large diameter is continuously raining and the wiper is operating continuously. At this entrance, the wiper blade itself is considerably wet. Also, a considerable amount of water is supplied to the windshield by the above dripping water. As a result, even in the situation without water supply by rainfall, the water wall pushed away by the blade is continuously formed. Therefore, in the invention described in the International Publication No. WO 91/03393, wiping by the wiper is continued despite the stop of actual rainfall.
In general, continuous operation of a wiper not in the rainfall situation to some extent is felt as extremely bothersome. In the invention described in International Publication No. WO 91/03393, control of intermittence is affected by the rainfall state immediately before even if the rainfall has stopped, and the situation that the continuous operation lasts and is felt bothersome may happen easily, which is a problem.
In the mean time, as another prior art, a method for detecting dynamic adhesion of raindrops (JP-A-2001-180447) and a method for evaluating fluctuation of an output signal of a light receiving element (JP-A-2002-277386) are presented by the inventors. Also, a method for detecting raindrops by comparison with a reference value (so-called threshold value method) (JP-A-61-37560, for example) and a method for detecting raindrops from an integrated value of light receiving element output (so-called integration method) (JP-A-4-349053, for example) are disclosed.